This invention relates to a method for reducing rub-off from a substrate, such as paper, having a toner image on only one side of the substrate by depositing a plurality of dots of a substantially clear phase change composition on the non-image bearing side of the substrate with said dots cumulatively covering an area of said non-image bearing side sufficient to reduce image rub-off from the image bearing side of an adjacent substrate. This invention further relates to the use of a phase change composition deposited on the side of a cover sheet that is contiguous with the image bearing side of an adjacent substrate to prevent rub-off from said adjacent substrate.
In electrophotographic copying processes, images are formed on selected substrates, typically paper, using small, dry, colored particles called toner. The thermoplastic toner is typically attached to a print substrate by a combination of heat and pressure using a fusing subassembly that partially melts the toner into the paper fibers at the surface of the paper substrate. Typically, in an electrophotographic printer, a heated fuser roller is used with a pressure roller to attach toner to a receiver and to control the surface image characteristics.
Fused toner images can be substantially abraded or xe2x80x9crubbed-offxe2x80x9d by processes such as duplex imaging, folding, sorting, stapling, binding, and filing and the like. Residue from this abrasion process causes objectionable and undesirable marks on non-imaged areas of adjacent pages or covers. This process, and image quality defect, are known as xe2x80x9crub-offxe2x80x9d and exist to varying extents in many electrophotographic copies and prints. The basic xe2x80x9crequirementsxe2x80x9d for generation of rub-off are a donor (toner image), a receptor (adjacent paper page, envelope, mailing label, etc.), a differential velocity between donor and receptor, a load between donor and receptor and pressing them together. Toner rub-off may be reduced by the use of tougher toner, lower surface energy toner materials (resulting in lower coefficient of friction), better fused toner, and a smoother toner image surface finish (causing increased image gloss.) Unfortunately, as described in detail hereinafter, there are undesirable consequences associated with each of the above rub-off reduction factors. Extensive efforts have been directed to the development of improved methods for reducing rub-off without modification of the fusing process.
According to the present invention, rub-off from a substrate bearing a toner image is reduced by a method for reducing rub-off by employing a first substrate having a front image bearing side and a back non-image bearing side, the method comprising: depositing a substantially clear phase change composition on the back side of the substrate which does not have a toner image as a plurality of dots, the dots cumulatively covering an area of said non-image bearing side sufficient to reduce rub-off from the toner image bearing side of a separate substrate that is adjacent to the back side of said first substrate.
The invention further relates to a method of reducing rub-off from a first substrate having a front side and a back side and a plurality of printer, copier, or digital copier produced toner images on said front side and no toner images on said back side, the method comprising: providing a cover substrate contiguous with said front side of said first substrate, depositing on the side of said cover substrate that is adjacent to said front side of said first substrate a substantially clear phase change composition as a plurality of dots, the dots cumulatively covering an area of the cover substrate sufficient to reduce rub-off from said front side of said first substrate.